A touch panel is an input device provided on a display panel such as a liquid crystal display panel and a plasma display panel to form a display device, and inputting information to the body of the display device by performing various types of operation on a screen of the display panel using a finger, a pen, etc.
Touch panels are classified into resistive-film, capacitive, infrared, ultrasonic wave, electromagnetic induction touch panels, etc., depending on their principles of operation. Of these, capacitive touch panels are relatively less likely to lose the optical characteristics of display devices, and are thus known as suitable for the display devices. In particular, projected capacitive touch panels are capable of multipoint detection of contact bodies such as fingers, and has thus excellent control characteristics of inputting complicated instructions.
A projected capacitive touch panel includes a touch region capable of detecting touch positions located in a region corresponding to a display region, and a picture-frame region in a region corresponds to a non-display region outside the display region. In the touch region, as electrodes for touch position detection, a plurality of first electrode groups, each of which includes a plurality of first electrodes aligned in one direction, are arranged in parallel, and a plurality of second electrode groups, each of which includes a plurality of second electrodes aligned in the direction orthogonal to the first electrode groups, are arranged in parallel. The first electrodes and the second electrodes are made of transparent conductive oxide such as indium tin oxide (hereinafter referred to as ITO) having low conductivity to make the screen of the display panel see-through.
Each adjacent pair of the first electrodes of the first electrode groups is connected by a first connecting portion. Each adjacent pair of the second electrodes of the second electrode groups is connected by a second connecting portion. The first connecting portion and the second connecting portion are made of transparent conductive oxide, similar to the first electrodes and the second electrodes. In each of intersections between the first electrode groups and the second electrode groups, the first connecting portion and the second connecting portion are provided with an interlayer insulating film interposed therebetween to be insulated from each other. The first electrode groups and the second electrode groups are electrically connected to different lead lines drawn in the picture-frame region from the touch region to a terminal region located at an end of the picture-frame region.
An internal connecting terminal, which is connected to one of the first electrode groups or the second electrode groups, is provided at the lead base end of each lead line. On the other hand, an external connecting terminal is provided at the top of each lead line. Each external connecting terminal is connected to a capacitance detection circuit, which applies AC voltages to the corresponding first and second electrode groups, and detects the capacitance at the portions corresponding to the first electrodes and the second electrodes. Each of the first electrodes, the second electrodes, and the lead lines is covered by a protective insulating film.
In this touch panel, when the insulating film is touched in the touch region, ones of the first electrodes and the second electrodes in the touch position are grounded via a capacitance generated between the electrodes and a contact body such as a finger, and via a human body. At this time, a change in the capacitance generated between the contact body and the ones of the first and second electrodes in the touch position is detected by the capacitance detection circuit. In this way, the touch position is detected based on the change in the capacitance.
In such a projected capacitive touch panel, lead lines are not necessarily transparent and are made of a highly conductive metal material such as copper (Cu) and aluminum (Al), which is used a conventional interconnect material. On the other hand, the internal connecting terminals and the external connecting terminals are made of transparent conductive oxide such as ITO as well as electrodes (i.e., first and second electrodes) for touch position detection. (See, for example, PATENT DOCUMENT1.)